Drill Stem Research Articles

ELECTRIC LOGGING APPLIED TO GROUND‐WATER EXPLORATION

A method is described for the determination of the quality of ground water in granular aquifers penetrated by rotary‐drilled holes electrically logged. Conventional techniques of electric‐log interpretation, to determine true bed resistivity from apparent resistivity values, are briefly described; and a method for converting water‐resistivity values into hypothetical chemical analyses is explained. The objective of the method is to narrow the limits of error in quality‐of‐water estimates based upon electric logs. Water‐well contractors are fully aware of the risks attendant in making drill‐stem tests in open hole, which is the method now employed to obtain representative samples of formation water. Packer failure results in contaminated samples; hole collapse may mean loss of drill stem, screen, and the hole. In the Gulf Coast where water‐well tests range in depth from 100 to 3,000 feet, methods that will eliminate at least a part of the need for drill‐stem tests deserve consideration. The paper deals also with methods of determining formation porosity in situ, which is an important factor in salt‐water‐encroachment problems.

Colloid Chemistry of Clay Drilling Fluids

It is only within the past 10 years that serious attempt appears to havebeen made to improve rotary drilling fluids by the application of theprinciples of colloid chemistry, although the use of chemicals to control therheological properties of clay slips has long been known in the ceramicindustry. The main difficulty apparently lay in the lack of a complete analysisof all of the functions of a drilling fluid in the drilling of the well, together with the lack of adequate consideration of how colloid science couldbe applied to secure these ends, and particularly how apparent antitheticalproperties of the fluid could be compromised. Thus one analysis1 of the manyrequirements of a drilling fluid proved conclusively that the viscosity shouldbe low, in order that cuttings and entrained gas might be eliminatedefficiently in the settling ditch, while the loss in carrying capacityaccompanying low viscosity could be regained by increasing either the densityof the mud or the upward velocity of the mud stream in the annular space of thewell, and the danger of sticking of the drill stem due to rapid settling incase of enforced suspension of drilling operations could be eliminated byenhancing the thixotropic properties of the fluid. The desired properties of the drilling fluid having thus been established, itwas a natural step to treat the fluid with viscosity-reducing chemicals, suchas salts of weak organic acids- for example, sodium tannate or gallate-and toadjust the pH to the alkaline side to such a degree of thixotropy as would give low viscosityand low yield point under the conditions of flow prevailing in the settlingditch, but rapid gelation and high yield point when quiescent in the annularspace during shutdowns. In fact, flow in the settling ditch should be justshort of turbulent while flow in the well, together with the flow of mud pastthe cuttings, is practically always turbulent. The use of chemicals other thanthose mentioned, such as Calgon (sodium hexametaphosphate) and certain otherphosphates together with sodium tannate, has now become standard practice andit is the consensus that this method of treatment has proved to be an importantstep in the development of the art of drilling oil wells. It is safe to assume that the application of colloid chemical principles canalso help in solving other outstanding problems of drilling fluids, such as thedevelopment of cheaper and more efficient viscosity reducers; the developmentof chemicals that do not lose their effectiveness in a short time duringdrilling operations; the finding of chemicals to preserve the plasteringproperties of muds when concentrated brines are encountered or in drillingthrough salt beds; improvement in the plastering properties of poor muds byfurther deflocculation, and, conversely, the prevention of excessivedeflocculation of certain marine shales sometimes encountered; the preparationof muds suitable for the successful drilling of heaving shale formations; thefinding of chemicals to treat the mud to prevent or to diminish lostcirculation; T.P. 1201

Petroleum Engineering as an Aid in Exploration Geology

Petroleum engineering contributes to geological knowledge by making and interpreting tests in drilling and producing wells. Core analysis, mud analysis, and electric logs indicate the presence of oil and gas, and a preliminary test may be made through the drill stem. Production and bottom-hole pressure tests prove the stability of the reservoir, indicate its extent and, in some cases, correlation between wells. Improved methods of completing and repairing wells have permitted exploitation of smaller and thinner reservoirs. Better testing methods and more economical drilling have extended the range of exploration both in area and in depth. Many of these advancements of petroleum engineering have been made in the past 3 years or less and promise to continue at an accelerate rate. There will be a parallel increase in their importance to the geologist in his solution of subsurface problems.

Theory and Practice of Directed Drilling

One of the most unusual oil-field engineering accomplishments of the pasttwo years is the development and rapid advance in the directed drilling ofwells. Directed drilling as referred to herein is the controlled steering ofthe drill stem in the required direction to a given location in the oilsand. The deliberate drifting of holes is an act so far removed from what has beenconsidered good drilling practice that all of the old questions of correlation, drillability and production difficulties are revived. Only a few years ago, during the boom days of Seminole and Santa Fe Springs, the crooked-holeproblem, as it was then called, occupied a primary position among the topics ofthe day in the fields of California and the Mid-Continent. The net result ofall the discussion and study at that time was the conclusion that oil wellsshould be drilled with as little deviation from the vertical as possible andthat crooked holes with elbows and dog legs were to be avoided because of thedrilling and producing difficulties encountered therein, but that manynonvertical holes were slanting or angling rather than crooked and were not aserious problem.

Effects of Temperature on the Viscosity of Some Gulf Coast Drilling Muds

With the introduction of rotary drilling in the Gulf Coast area, somethirty-two years ago, and its subsequent spread to other producing localitiesin the United States, there has been a constant change in the design ofequipment. Only the general features remain, namely the rotating drill stem andthe circulating mud. Only recently have the properties of mud and theirbehavior received attention from petroleum engineers, but circulating problemsin present deep drilling demand further study and understanding. It is the purpose of this investigation to determine the relative changes inthe apparent viscosity of muds with changes in temperature and to discoverother physical effects due to heat. Very little information has been published regarding the effects of temperatureon the viscosity of drilling muds. Maust states: "The viscosity of mostmuds is decreased on heating, but the interesting thing is that the degree offlocculation is also increased on heating. There will be a greater tendency toseal off formations at high temperatures than at low temperatures." Withregard to the effect of temperature on viscosity and yield point, Herrickstates: "The variation of yield point and viscosity of mud with temperature….. is not very clearly brought out by the data available. Both appear todecrease slightly with increasing temperature up to 2000 F." Theexperimental results presented in this paper further emphasize thispoint. Two types of viscosimeters are available for measuring the apparent viscositiesof drilling muds: the efflux tube type as used by Herrick and Marsh, and thetorsional type such as the McMichael or the Stormer viscosimeters.

A Modern Rotary Drill

Published in Petroleum Transactions, AIME, Volume 52, 1916, pages 620–626. In drilling for water and oil to reasonable depths through the generally soft yielding clay and sand formation of the Coastal Plain of Texas, Louisiana, and Mississippi, the rotating method of drilling was adopted, ' principally on account of the easy and quick penetration, and the low cost of the drilling plant. In favorable ground, free of heavy gravel and rock strata, as much as 1,600 ft. has been drilled in less than 36 hr., although such performances were of course rare. Hydraulic rotary drilling, or, as it is now called, rotary drilling, was used in the above States as early as 1880. The plant consisted of an ordinary derrick, a 25-h.p. boiler, a small hoist, a steam pump, and a water swivel with hose attachment, and an ordinary flat diamond-pointed bit. The successful drilling in of a phenomenal oil well by this process on Spindletop, near Beaumont, Texas, on Jan. 10, 1901, and the ascertained impracticability of drilling subsequent wells in the same locality by other methods (owing principally to heavy quicksand under pressure from be- low), brought rotary drilling into great prominence, practically to the exclusion of any other process throughout the Coastal Plain, and later on elsewhere. The method, as its name implies, involves the rotation of a pipe by means of machinery placed on the derrick floor. A drill bit attached to the lower end cuts a clearance for the drill pipe, with much the same motion and effect as an auger. Water forced through the drill pipe by means of a pump, and escaping through the bit, removes the cuttings and returns to-the surface outside the drill pipe. In this manner the hole is kept open, permitting the drill stem to rotate freely. The pressure of the column of muddy water holds up the walls of the hole until it has been cased. Practically all the wells of the Gulf coast region, numbering nearly 10,000, have been drilled with this system. During the last five years its use has been extended to many other States and countries. T.P. 051–41